Puerto Rico's nonvoting representative in the U.S. Congress said Sunday that Hurricane Maria's destruction has set the island back decades, even as authorities worked to assess the extent of the damage.

"The devastation in Puerto Rico has set us back nearly 20 to 30 years," said Puerto Rico Resident Commissioner Jenniffer Gonzalez. "I can't deny that the Puerto Rico of now is different from that of a week ago. The destruction of properties, of flattened structures, of families without homes, of debris everywhere. The island's greenery is gone."

Puerto Rico's National Guard diverted an oil tanker that broke free and threatened to crash into the southeast coast, said Gov. Ricardo Rossello, and officials still had not had communication with nine of 78 municipalities.

"This is a major disaster," he said. "We've had extensive damage. This is going to take some time."

The death toll from Maria in Puerto Rico was at least 10, including two police officers who drowned in floodwaters in the western town of Aguada.